feat(fonts): updated font weights for ds base token alignment

[harpalsingh]

Proposed behaviour

Updating the fonts so that we see the following range:

• 700 - the new thickest weight relative number
• 500 - the new "bold" weight
• 400 - this is the same as currently implemented

Current behaviour

The current weights are:

• 900
• 700
• 400

Checklist

• Commits follow our style guide
• Related issues linked in commit messages if required
• Screenshots are included in the PR if useful
• All themes are supported if required
• Unit tests added or updated if required
• Playwright automation tests added or updated if required
• Storybook added or updated if required
• Translations added or updated (including creating or amending translation keys table in storybook) if required
• Typescript d.ts file added or updated if required
• Related docs have been updated if required

QA

A note for QA - you should see NO DIFFERENCE with components. Though the title segments in Storybook might be thicker, not sure how we manage that, but no component should look different from what they do today, that is the QA part.

Additional context

Testing instructions